The present invention relates to an image processing apparatus capable of detecting a face from an image.
Regarding detecting human faces in an image, there has been known a technique regarding a face detection system, which performs learning on the basis of a plurality of sample image data, to determine and detect whether or not an image region within a detection window set in the image is a face region (refer to JP-A-2009-32018).
In the photographed image, faces in various poses may exist. For example, the photographed image may capture not only faces (frontal faces) which are directed to the front or substantially to the front but also faces (profile faces) which are turned by a certain degree in the horizontal direction and faces (tilted faces) for which the lengthwise directions are tilted with respect to the image. In such a situation, when the faces turned to various directions are intended to be detected, two methods are mainly used. The first method detects faces (the faces and the poses thereof) from the inside of the image by use of a single face detector which learns on the basis of an enormous volume of sample image data so as to be able to detect faces in all poses. The second method provides a face detector (a frontal face detector), which learns only frontal face detection, another detector (a profile face detector), which learns only profile face detection, and the like and individually applies the frontal face detector and the profile face detector to the image.
In the first method, it is difficult to generate one face detector capable of accurately detecting the poses of faces in all poses. Hence, problems arise in low detection accuracy and slow detection speed. Therefore, the second method is employed in order to solve the problems of the corresponding first method. However, in the second method, it is problematic that a plurality of detection results can be generated from one face. Specifically, when the frontal face detector is used for the person's face captured in an image, one face may be detected (a frontal face), and when the profile face detector is used therefor, another face may be also detected (a profile face). That is, if poses of a plurality of faces are detected, it is problematic as to which detection result is correct and should be adopted.